NOT reverse the boolean "true" into "false". This can be used in IF/THEN construct.

Use of non-numerical terms in conjunction with NOT causes a ?TYPE MISMATCH ERROR IN line. In the case of bitwise NOT operations the range of −32768 thru 32767, or −$8000 thru $7FFF in hexadecimal — terms outside of this range will raise an ?ILLEGAL QUANTITY ERROR IN line. If either of the terms are absent, a ?SYNTAX ERROR IN line will occur.

In the case of bitwise NOT operations, both terms are evaluated as 16-bit signed integers, and thus cannot exceed the range of −32768 thru 32767, or −$8000 thru $7FFF in hexadecimal — terms outside of this range will raise an ?ILLEGAL QUANTITY ERROR IN line. If either of the terms are absent, a ?SYNTAX ERROR IN line will occur.

Note that in BASIC on the C-64, the boolean value "true" is represented by the integer −1, which is all bits set in the 16-bit signed format, while the value "false" is represented by the value 0, or all bits clear.

IF NOT A=1 AND NOT C=0 THENPRINT "HALLO" (HALLO is printed, when the variable A is unequally 1 and the varibale C is unequally 0.)
IF NOT A$<>"Saturday" THEN PRINT A$ (A$ is printed, when the contain of the variable is equal Saturday)